In the previous three-year period we completed the primary structure determination of prothrombin (including thrombin). The present project proposes to complete the primary structures of plasminogen, antithrombin-III and hirudin, and also to provide material or crystals for tertiary structure determination in this field. A useful substrate for specific determination of factor Xa has already been developed on the basis of information from the prothrombin structure, and this line of development is proposed to be continued.